Image DCT coefficient statistics and their use in blind noise variance estimation

Statistical characteristics of DCT coefficients in 8×8 blocks of noise-free and noisy images are considered. It is shown that DCT coefficients obey generalized Gaussian distribution where its parameters are individual for different DCT coefficients and depend upon image and noise properties. Analysis of statistics is carried out for all image blocks and separately for blocks recognized as homogeneous. Several approaches to robust scale estimation of DCT coefficients are discussed and the corresponding techniques for blind estimation of noise standard deviation (variance) are proposed and studied. It is demonstrated that joint processing of estimates obtained from a set of homogeneous blocks produces less biased estimation.